Plastic spring-loaded piston

ABSTRACT

A spring-loaded piston is produced from plastic, particularly by injection molding. The spring-loaded piston is developed in the area of a connection to a piston or piston rod such that tilting of the spring-loaded piston with respect to the piston rod is prevented and a sufficiently firm connection is ensured. In addition, the spring-loaded piston  1  may include a reinforcing insert by which clearly higher forces can be transmitted while maintaining smaller wall thicknesses than in conventional spring-loaded pistons. Also, the seat or contact surface in the spring-loaded piston is constructed for supporting the preloaded spring such that possibly occurring radial forces do not have any negative influence on the functionality of the spring-loaded piston.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to co-pending U.S. patent application Ser.No. 10/178,777, entitled “Plastic Spring-Loaded Piston With Insert”.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a spring-loaded piston forspring-loaded brake cylinders, particularly for brake cylinders ofcommercial vehicles.

Service brake cylinders, spring-loaded brake cylinders as well ascombined service brake and spring-loaded brake cylinders, frequentlycalled “combination cylinders” are known from practice. Brake cylindersof this type are used for the operation of brake systems of vehicles,particularly of commercial vehicles. In the case of known purespring-loaded brake cylinders, a prestressed preloaded spring acts byway of a spring-loaded piston upon a piston rod, so that a brake can beoperated in an application. The service brake part of a service brakecylinder or of a combination cylinder, in the case of brake cylindersknown from practice, generally contains a diaphragm which can be actedupon by compressed air and which acts with respect to a plate and anoperating tappet connected with the plate. In the case of a combinationcylinder, the spring-loaded brake part is saddle-mounted on the servicebrake part. Such a saddle-mounted spring-loaded brake part is described,for example, in German Patent document DE 198 30 154 A1. Here, a pistonrod of the spring-loaded brake part, which is connected with thespring-loaded piston, acts upon the diaphragm of the service brakecylinder when actuated by the preloaded spring and transmits via theplate of the service brake cylinder, the spring-loaded brake force uponthe operating tappet. For this purpose, the preloaded spring istensioned beforehand when the spring-loaded chamber is acted upon bycompressed air.

Such spring-loaded brake cylinders have a spring-loaded piston cast ofaluminum or zinc. However, these cast components have the significantdisadvantage that, after the casting, finishing steps are alwaysrequired for the removal of possible burrs or for evening-out thesurfaces. Furthermore, frequently required bores for fastening deviceshave to be made, for example, in a cutting manner, or seat surfaces forsealing rings or slide rings or the like have to be worked-in. Also,these spring-loaded pistons made of aluminum or zinc have thedisadvantage that, as a result of not completely avoidable moisture,they are subjected to corrosion or similar aging processes, which mayfinally lead to a malfunctioning. Finally, the manufacturing ofspring-loaded pistons as an aluminum or zinc casting is relativelyexpensive, and it is another disadvantage that the casting molds aresubjected to high wear, and therefore only limited quantities can beproduced.

In addition, the spring-loaded pistons known from practice areconstructed in one piece with the piston rod. As a result, differentcasting molds are required for different piston rod lengths forproviding different strokes, which again has a negative effect on themanufacturing costs. In this case, the known piston rods are necessarilyalso made of aluminum or zinc castings, so that these are also subjectedto the above-mentioned risks of corrosion or aging.

It is therefore an object of the present invention to provide aspring-loaded piston which can be produced at lower cost without anysignificant finishing expenditures. In addition, it should be possibleto minimize the above-mentioned corrosion and aging risks.

It is another object of the present invention to provide a spring-loadedpiston having devices that permit an optimal connection between thespring-loaded piston and a separate piston rod.

These objects are achieved by a spring-loaded piston for a spring-loadedbrake cylinder, particularly of commercial vehicles, wherein thespring-loaded piston is made of plastic.

According to the invention, a plastic is selected as the material forproducing the spring-loaded piston. Contrary to existing prejudices withrespect to plastic as a material considered useless for spring-loadedpistons in comparison to aluminum and zinc, tests have surprisinglyshown that spring-loaded pistons made of plastic can have operatingcharacteristics which are just as good as those of conventionalspring-loaded pistons. Also surprisingly, the braking forces achievedthereby are no less than the braking forces achievable using theconventional spring-loaded pistons. Furthermore, the expected usefullife of a spring-loaded piston made of plastic is against allexpectations even above the expected useful life of a conventionalspring-loaded piston.

In that a spring-loaded piston made of plastic is suggested for thefirst time, which can be made, for example, as a plastic injectionmolded part, the clearly higher quantities that can be made by a plasticinjection mold can be advantageously utilized for increasingproductivity, in which case rates of increase of 10 to 20 times incomparison to the conventional aluminum or zinc castings can beimplemented without additional expenditures. Furthermore, when thespring-loaded piston is made of plastic, a high-expenditure finishingcan, as a rule, be eliminated. Plastic injection molded parts havesmooth surfaces from the start. Burrs, which have to be removedsubsequently at high expenditures, normally do not occur in the case ofplastic injection molded parts. The manufacturing costs of aspring-loaded piston made of plastic can therefore clearly be reduced incomparison to the manufacturing costs of conventional spring-loadedpistons cast of aluminum or zinc.

Furthermore, the first-time selection of plastic as the material forproducing the spring-loaded piston according to the invention has theadditional advantage that a spring-loaded piston made of plastic hasgreater useful life and is resistant to corrosion that may occur becauseof possibly existing moisture.

In addition, the use of plastic for producing the spring-loaded pistonalso has the additional advantage of a clear weight reduction incomparison to the aluminum or zinc casting technology. This reduces theexpenditures with respect to handling during the manufacture of aspring-loaded piston produced as an injection molded part of a plasticand contributes to lower transport costs of the produced parts becauseof their smaller measurements.

Furthermore, a spring-loaded piston made of plastic has the additionaladvantage that seats for sliding rings, seals, or the like have asufficiently high surface quality and/or fitting precision so that theworking-in of such fitting surfaces for sliding rings, seals or thelike, which is expensive specifically in the case of conventionalaluminum or zinc castings, can be eliminated. This, in turn, isreflected in reduced machining time as well as in lowering of costs.

Not least, the manufacturing of a plastic spring-loaded piston accordingto the invention permits a noticeable noise reduction during the furthermachining since its hollow plastic body does not produce any significantnoise in contrast to a metallic hollow body. This circumstance isparticularly noticeable by the workers entrusted with the integration ofthe brake cylinder, in that the workplace quality is improved.

Advantageous further developments of the invention are described herein.

Thus, in a preferred embodiment, the spring-loaded piston according tothe invention has a ring-shaped shoulder for receiving a piston or apiston rod. In this case, the ring-shaped shoulder has a definedlongitudinal dimension in the axial direction in order to provide asufficient hold as well as good guidance to the piston or the pistonrod. This shoulder is used as a contact surface for a piston to beinserted or a piston rod to be inserted. As a result, it isadvantageously ensured that the piston or the piston rod and thespring-loaded piston exactly maintain a predefined position.

This positional accuracy is further increased in that, in anotherpreferred embodiment, the receiving section of the spring-loaded pistonfor receiving a piston or a piston rod has, for example, a secondring-shaped shoulder molded thereto for an engagement in a correspondingreceiving device of the piston or for an engagement in the tube-shapedpiston rod. In addition to tube-shaped shoulders, shoulders having othercross-sections may also be used here.

Furthermore, in another preferred embodiment, the spring-loaded pistonmay have supporting elements extending parallel to the longitudinal axisof the spring-loaded cylinder. These supporting elements are arranged,for example, in a ring shape and are preferably molded to thespring-loaded piston in one piece to the second ring-shaped shoulder.The supporting elements may engage in a corresponding receiving deviceof the piston or in the tube-shaped piston rod. This further increasesthe positional stability of the piston or of the piston rod in relationto the spring-loaded piston and can further reinforce the connectionbetween these two components. In addition, material can advantageouslybe saved in this manner when the inner ring-shaped shoulder has tonguesor lugs extending in the axial direction, instead of having an alsoconceivable solid-wall, tube-shaped or cylindrical design. The tongs orlugs can, in turn, advantageously be used simultaneously as a receivingdevice for a standardized, short release device so that the latter canbe integrated in the spring-loaded piston in a space-saving manner.

To increase the introduction and/or transfer of force from thespring-loaded piston into the piston rod or the piston, a furtherembodiment provides radially extending webs as reinforcing ribs in theforce diversion area.

Furthermore, in a preferred embodiment, the piston or the piston rod ismade of plastic, particularly in an extruded manner. Since it ispossible for not only the spring-loaded piston to be made of plastic,but also that it may be a component separate from the piston rod, as aresult of a free combination possibility of a certain spring-loadedpiston type with a plurality of pistons or piston rods differing, forexample, with respect to their length or their diameter, a large numberof spring-loaded pistons can advantageously be produced withoutadditional costs having an integrated piston or an integrated piston rodof different strokes. In addition, the spring-loaded piston according tothe invention, as a separate part, can be installed more easily and isalso distinguished by a simpler handling. Furthermore, as required,materials, such as aluminum or zinc castings, can also be used for thepiston or the piston rod. As a result, existing piston rods can still beused, which additionally reduces the manufacturing costs.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three-dimensional, cut-open lateral view of a spring-loadedpiston according to the invention with a piston rod integrated therein;and

FIG. 2 is a sectional enlarged view of the center area of thespring-loaded piston illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three-dimensional sectional view of an embodiment, shown asan example, of spring-loaded piston 1 according to the invention. Thespring-loaded piston 1 produced of plastic has an inserted piston rod 2,whose length may be adapted according to the required stroke and whichmay be produced of a suitable material, such as aluminum or zinc or, forexample, as an extruded part made of plastic. A web 4 constructed as anoutward protuberance extending around the piston in a ring-shaped manneris visible at the outer circumference of the spring-loaded piston 1. Theweb 4 can be used as a shoulder for supporting a slide ring (not shownin detail) or can, for example, itself operate as a slide ring.Furthermore, sealing devices, which are not shown in detail, may besupported against the web 4, if required. The radially exterior,surrounding section of the spring-loaded piston wall can therefore alsobe called a guide section 5. Inside the ring-shaped cavity 6 of thespring-loaded piston 1 radially bounded by the guide section 5, whichcavity 6 is bounded in the axial direction X in turn by the so-calledpiston plate section 7, a preloaded spring is situated (which is notillustrated in detail in FIG. 1). The last turn of the preloaded springis supported against a bearing area or a bearing surface 8 of the platesection 7. For diverting radial forces of the preloaded spring (which isnot shown in detail), humps, shoulders, or shoulder sections 10 areprovided which project into the interior of the spring-loaded piston 1and therefore face the cavity 6. Also, in this embodiment, the bearingsurface 8 has a profiled construction.

As illustrated particularly in FIG. 2, which is an enlarged detail ofFIG. 1, the last turn of the preloaded spring 12 (illustrated there as asectional view), rests radially on the inside against the curved contour14 of the spring-loaded piston 1. In addition, the last turn of thepreloaded spring 12 rests radially on the outside against the shoulder10. In the axial direction X of the spring-loaded piston 1, thepreloaded spring 12 rests form-fittingly against the interior contour ofthe spring-loaded piston 1, the contact surface 8 being profiled in thisarea. In the embodiment illustrated here, the contact surface 8 hasthree grooves 16, 16′ and 16″ extending in a ring-shaped surroundingmanner (see FIG. 1 as well), between which grooves 16, 16′ and 16″, thewebs 17 and 17′, respectively, are situated. The webs protrude into thecontour of the adjoining preloaded spring 12 and are preferablydeformable, which permits an adaptation of the contact surface 8 to thecontour of the preloaded spring during the running-in of thespring-loaded brake cylinder. In this manner, it is ensured that theradial forces of the preloaded spring, which are known from conventionalspring-loaded pistons and can normally not be completely avoided, can bediverted into the spring-loaded piston 1 at least such that no negativeeffects need to be feared on the sealing devices, which are normallystressed only slightly in the radial direction. Or, in the ideal case, agenerating of these radial forces is largely avoided.

In FIG. 1, the inner section of the spring-loaded piston 1, whichreceives a piston or the piston rod 2, is marked as area 18. This areahas a seat 20, which extends in a surrounding manner in a ring shape.The seat 20 changes radially toward the outside into the piston wallthat surrounds the preloaded spring, which piston wall is sometimes alsocalled a piston shirt. The radial inner section of this piston wall hasthe reference number 21. The piston rod 2 is supported against thering-shaped seat 20. In this case, the piston rod 2 is held from theoutside by a ring-shaped shoulder 22. Another ring-shaped shoulder 24supports the piston rod 2 from the inside. The inner shoulder 24 isadjoined by tongues or lugs 26, which are molded on in one piece andwhich extend in the axial direction X. In the embodiment illustratedhere, six of such lugs 26 are provided. Instead of these lugs 26, atube-shaped extension of the ring-shaped shoulder 24 may be provided.However, the lugs 26 have the advantage that material can be saved andthey can generate a certain elastic prestress. Inside the cavity definedby the piston rod 2 and the lugs 26, a release device can be integrated(not shown in detail). This release device can then be supported againstthe recesses 28 of the lugs 26. The recesses 28 can also be used asabutments for tensioning devices. For reinforcing the ring-shaped seat20, the seat 20 has radially oriented inner as well as outer supportingribs 30 and 32, respectively.

In the embodiment of a spring-loaded piston 1, which is illustrated ofan example, in FIG. 1 as well as in FIG. 2 (enlarged cutout of FIG. 1),an insert 34 is provided for reinforcing the piston shirt. Thereinforcement 34 may be produced of a material which can be stressedparticularly well under tension, such as steel or the like, to form, forexample, a steel insert. In this case, the insert 34 follows the contourof the piston shirt. It starts with a bent curve in the area of thecorresponding bent contour 14 of the wall of the spring-loaded piston 1and then extends there subsequently approximately concentric to thelongitudinal direction or main axial direction of the spring-loadedpiston 1 or at a certain angle slightly inclined thereto, and then bendsaway in a first area 36 by approximately 45°, in order to bend intoanother section 38 again by approximately 45° and end in a ring-shapedsection 40. With the exception of small partial areas, the insert 34will be almost completely enclosed by the wall of the spring-loadedpiston 1, particularly by the wall of the piston shirt.

During the manufacturing of the spring-loaded piston 1, plastic materialis sprayed around the insert 34. In the end area 40 in which the insert34 ends in the support 20, the steel insert 34 has at least onenose-type protuberance or shoulder 42, which is used for centering thepiston rod 2. The piston rod 2 is supported in the spring-loaded piston1 on the face-side against the end section 40 of the steel insert 34. Aforce introduced by the preloaded spring 12 in the bearing area 8 istransmitted by way of the piston shirt and the steel insert 34integrated therein into the ring-shaped seat 20 and is transmitted bythe latter to the piston rod 2.

A tilting of the spring-loaded piston 1 with respect to the piston rod 2is excluded by the integration of the piston rod 2 within thering-shaped shoulder 22 and of the second ring-shaped shoulder 24 aswell as the lugs 26. The outer contour or the guide section 5, thepiston plate section 7 as well as the piston shirt of the spring-loadedpiston 1 are produced with the ring-shaped shoulder 22 and thering-shaped shoulder 24 as well as the lugs 26 from one piece ofplastic, which is indicated in FIG. 1 as well as FIG. 2 by the use of auniform hatching.

The present invention therefore creates for the first time aspring-loaded piston which is manufactured, for example, by injectionmolding of plastic. Furthermore, in the area of the connection to thepiston rod, the spring-loaded piston according to the invention isfurther developed such that a tilting of the spring-loaded piston withrespect to the piston rod is substantially prevented, and a firmconnection is ensured between the spring-loaded piston and the pistonrod. In addition, the spring-loaded piston according to the inventionhas a reinforcing insert, by which clearly higher forces can betransmitted in the case of smaller wall thicknesses than in the case ofconventional spring-loaded pistons. Not least, the seat or the bearingsurface in the spring-loaded piston for supporting the preloaded springis constructed such that radial forces potentially occurring have nonegative influence on the functionality of the spring-loaded piston.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A spring-loaded piston for a spring-loaded brakecylinder of a commercial vehicle, wherein the spring-loaded piston is aplastic spring-loaded piston; and wherein the spring-loaded pistonincludes a seat between a first ring-shaped shoulder and a secondring-shaped shoulder adapted to receive a piston or piston rod.
 2. Thespring-loaded piston according to claim 1, wherein the piston isintegrated with the first ring-shaped shoulder and the secondring-shaped shoulder.
 3. The spring-loaded piston according to claim 1,wherein the first ring-shaped shoulder has a defined longitudinaldimension in an axial direction of the spring-loaded brake cylinder. 4.The spring-loaded piston according to claim 2, wherein first ring-shapedshoulder has a defined longitudinal dimension in an axial direction ofthe spring-loaded brake cylinder.
 5. The spring-loaded piston accordingto claim 1, further comprising supporting elements extendingsubstantially parallel to a longitudinal axis of the spring-loaded brakecylinder, the supporting elements being arranged in a ring and beingmolded to the second ring-shaped shoulder in one piece; and wherein thesupporting elements are adapted to engage in the piston or the pistonrod.
 6. The spring-loaded piston according to claim 2, furthercomprising supporting elements extending substantially parallel to alongitudinal axis of the spring-loaded brake cylinder, the supportingelements being arranged in a ring and being molded to the secondring-shaped shoulder in one piece; and wherein the supporting elementsare adapted to engage in the piston or the piston rod.
 7. Thespring-loaded piston according to claim 3, further comprising supportingelements extending substantially parallel to a longitudinal axis of thespring-loaded brake cylinder, the supporting elements being arranged ina ring and being molded to the second ring-shaped shoulder in one piece;and wherein the supporting elements are adapted to engage in the pistonor the piston rod.
 8. The spring-loaded piston according to claim 1,further comprising an aluminum piston rod received by the spring-loadedpiston.
 9. The spring-loaded piston according to claim 2, furthercomprising an aluminum piston rod received by the spring-loaded piston.10. The spring-loaded piston according to claim 3, further comprising analuminum piston rod received by the spring-loaded piston.
 11. Thespring-loaded piston according to claim 7, further comprising analuminum piston rod received by the spring-loaded piston.
 12. A methodof manufacturing a spring-loaded piston for a spring-loaded brakecylinder of a commercial vehicle, the method comprising the acts of:forming an injection mold of the spring-loaded piston to include a seatbetween a first ring-shaped shoulder and a second ring-shaped shoulderadapted to receive a piston or piston rod; and injection molding withplastic the spring-loaded piston using the injection mold.
 13. Themethod of making the spring-loaded piston according to claim 12, furthercomprising the act of extrusion molding a piston rod; and inserting theextrusion molded piston rod in the seat of the injection moldedspring-loaded piston.